Describe to students what
contour lines are. Our "Mapping
Potato Island" activity is an excellent way to introduce this
concept. While a topographic map has contour lines that describe the
shape of the land surface, a bathymetric map has contour lines that
describe the shape of the ocean floor. Bathymetric maps, like topographic
ones, use sea level as a reference point.

Familiarize students with
the graph at the top of their worksheets. This graph describes sea level
change over time. Global sea level changes in recent geologic history
have been due to repeated formation and melting of glaciers which move
water onto land, away from oceans.

Students use the graph to
find the sea level at various times in the past (Answers: -124 meters;
-75 meters; approx -40 meters; approx -135 meters) then draw ancient
coastlines onto their bathymetric map following contour lines.

The final question involves
the likely age of archeological sites that were once along a coast.
If it must be less than 20,000 years ago (because there were no people
living in that area before that time), then the answer must be about
10,000 years ago.

BACKGROUND INFORMATION:

Contour lines are
imaginary lines that connect places of equal elevation. If you were taking
a hike along a hillside and not walking either uphill or downhill, you
would be walking on a contour line. When contour lines are close together,
the slope is very steep. When contour lines are far apart, the slope is
very shallow. Maps that show the shape of the ocean floor with contour
lines are called bathymetric maps.

Sea level change has happened
at various times in Earth history. Global sea level can rise because glaciers
melt, adding water to the oceans, or when plate tectonic movements shallow
the ocean basins displacing water onto the edges of continents. It is
a natural process that has gone on since there have been oceans on Earth!
Over recent geologic history, sea levels have changed rapidly by geologic
standards due to the repeated formation and melting of glaciers.